As it promised, HP is taking on Amazon's cloud-computing service—with an open-source approach that allies it with Rackspace.

It officially opened a cloud-storage service today that goes head to head with Amazon Web Service's S3. HP's Object Storage lets companies store data in the cloud for apps, websites, backup services, and other offerings.

"We've also got the type of global footprint and [a service-level agreement] and a business-grade point of view that understands the enterprise," he said. "That's what we're betting on."

HP is also different from Amazon in that it's using an open-source cloud operating system called OpenStack. That means it will be contributing the code it used to build its content-delivery service back to the OpenStack project. Other Openstack cloud providers can use it, too.

While HP and Rackspace are in some sense competing for customers' business, by using OpenStack, they're pursuing a unite-and-conquer strategy. The idea is that enterprises can hire any of these companies and easily move their apps and data between them if they want more than one cloud provider. It's not unlike the Windows and Linux ecosystems, where companies can easily choose between multiple hardware providers.

Amazon, which has been taking heat for outages, can't make the same claim. Its cloud runs the same homegrown software used for its own website—so it's proven, but proprietary to Amazon.